aortic valve, a valve in the heart between the left ventricle and the aorta. It is composed of three semilunar cusps that close in diastole to prevent blood from flowing back into the left ventricle from the aorta. The three cusps are separated by sinuses that resemble tiny buckets when they are filled with blood. These cup-shaped flaps grow from the lining of the aorta and, in systole, open to allow oxygenated blood to flow from the left ventricle into the aorta and on to the peripheral circulation. Compare mitral valve, pulmonary valve, tricuspid valve.
